1. Field of the Invention
The present invention relates to optical disc playback apparatuses and, more specifically, to an optical disc playback apparatus for displaying, on a television, an on-screen message in the font having resolution suitable for a type of an optical disc being played back or the display resolution of data recorded thereon.
2. Description of the Background Art
Recently, video CD players which are CD players incorporated with MPEG1 (Moving Picture Coding Experts Group1) decoding feature are widely available. Such video CD players are capable of reproducing images and sounds for maximum of 74 minutes from moving picture data and audio data recorded on video CDs (hereinafter abbreviated as VCDs) and Karaoke CDs, wherein such data is digitally compressed by MPEG1 technique. Further, CVDs (China Video CDs) and SVCDs (Super Video CDs) with higher quality of image and audio data are commercialized especially focusing on Chinese market. The CVDs and the SVCDs are realized with MPEG2 (Moving Picture Coding Experts Group2) digital video decoding feature instead of MPEG1, and can be played back without any modification on mechanism such as optical pickup, servo technique, and signal processing technique for the MPEG1.
Mainly in Japanese and US markets, DVD players incorporated with the MPEG2 decoding feature are commercialized. The DVD players are capable of reproducing maximum of 133 minute high-quality moving pictures with high-resolution defined horizontally by 702 dots and vertically by 480 lines, together with high-quality sound. In addition to the higher quality of reproduced images and sounds, advanced features are achieved in these VCD players and DVD players. Such advanced features are quite convenient for sophisticated users who are familiar with such features to enjoy various functions. On the other hand, for ordinary users, the players and its peripherals achieving such advanced features are difficult to use due to the complicated operation required. To ease the user's inconvenience caused by the complicated operability, the VCD players and DVD players recently adopt an On-Screen Display (hereinafter abbreviated as OSD) function. The function is for displaying information on a monitor for user's easy operation. Such information indicates input information corresponding to user's operation, an elapsed time after start of reproduction, a status of the player during reproduction, a special reproduction function, and a type of optical disc. The displayed information is referred to as an on-screen message (hereinafter abbreviated as OSM).
Hereinafter, by referring to FIGS. 11 and 12, examples of conventional optical disc playback apparatuses are described. In FIG. 11, a first example of the conventional optical disc playback apparatus is shown. In a conventional optical disc playback apparatus OPC1 of this example, an optical disc Od, typically a music CD, is fixedly placed on a spindle motor 72 for rotation. An optical pickup 73 applies a laser beam Lb onto the recording surface of the rotating optical disc Od to read out data therefrom as digital signals.
An optical servo controller 74 executes a servo-control of the spindle motor 72 and the optical pickup 73. A digital signal processor 75 demodulates the digital signals from the optical pickup 73 to convert the signals into sub-code information, control information, a sequence of CD-DA signals unique to the music CD, and a sequence of other signals. Based on the sub-code information and the control information from the digital signal processor 75, a system controller 76 determines the type of the optical disc being played back and detects a system error such as track jump and focus error of the laser beam Lb.
An information signal sequence separator 79 separates the digital signal sequences supplied from the digital signal processor 75 into the CD-DA signal sequence and the signal sequence other than that.
An MPEG decoder 78 receives the CD-DA signal sequence and the signal sequence other than that from the information signal sequence separator 79. The MPEG decoder 78 outputs the received signal sequence as it is by using memory 77 as buffer memory upon receiving the CD-DA signal sequence. On the other hand, if MPEG decoder 78 receives the signal sequence other than the CD-DA signal sequence, the system controller 76 reads sequence header information included in disc information read from the optical disc Od. Based on the sequence header information, the system controller 76 determines a type of the optical disc Od, i.e., VCD, SVCD, or DVD, and further determines whether the video recorded thereon (signal sequence other than the CD-DA signal sequence) is in the PAL format or in the NTSC format.
Further, by using the memory 77 as buffer memory, the MPEG decoder 78 converts the video signal sequence (signal sequence other than the CD-DA signal sequence) in real time into a decoded digital signal sequence. If the system controller 76 determines that the optical disc Od is a VCD, the MPEG decoder 78 decodes the reproduced video signal sequence with MPEG1 technique. If the system controller 76 determines that the optical disc Od is an SVCD or DVD, the MPEG decoder 78 decodes the reproduced video signal sequence with MPEG2 technique. Thereafter, if the video is in the PAL format, the decoded video signal sequence is converted into a decoded digital signal sequence in the PAL format, and if in the NTSC format, into a decoded digital signal sequence in the NTSC format.
In other words, if the video signals recorded on a VCD are in the NTSC format, an image is reproduced in the resolution of 352 dots by 240 lines, and if in the PAL format, in the resolution of 352 dots by 288 lines.
If the video signals recorded on an SVCD are in the NTSC format, an image is reproduced in the resolution of 480 dots by 480 lines, and if in the PAL format, in the resolution of 480 dots by 576 lines.
If the video signals recorded on a DVD are in the NTSC format, an image is reproduced in the resolution of 720 dots by 480 lines, and if in the PAL format, in the resolution of 720 dots by 576 lines.
An on-screen display controller 7A converts character data and character display information read out from the system controller 76 into a digital character signal sequence to display an on-screen message. Font characters of the on-screen message remains unchanged in the resolution of 12 dots by 18 lines regardless of the resolution of the reproduced image.
A video signal D/A converter 7B converts the decoded digital signal sequence from the MPEG decoder 78 and the digital character signal sequence from the on-screen display controller 7A into analog video signals. An audio signal D/A converter 7C converts the CD-DA signal sequence from the MPEG decoder 78 into analog audio signals.
The playback operations of the optical disc playback apparatus OPC1 are described with respect to a music CD and other type of optical disc, respectively. For playing back the music CD, the digital signal processor 75 starts demodulation of the digital signals and then outputs the control information and the sub-code information.
When the system controller 76 determines that the signal sequence is the CD-DA signal sequence based on the control information and the sub-code information, the system controller 76 judges that no video signal sequence is recorded on the optical disc Od. In such case, the system controller 76 transmits a control instruction instructing the digital signal processor 75 to output border color signals (normally blue-back) in the NTSC format instead of the video signals. The system controller 76 further outputs the character display information and the character data to the on-screen display controller 7A.
The system controller 76 monitors a system error such as track jump and focus error. Whenever such error occurs, the system controller 76 instructs the optical servo controller 74 so that the optical pickup 73 and the spindle motor 72 return to initial states thereof.
The MPEG decoder 78 receives the CD-DA signal sequence from the digital signal processor 75, and outputs the same by using the memory 77 as buffer memory. The MPEG decoder 78 also converts the border color signals in the NTSC format from the digital signal processor 75 into the decoded digital signal sequence.
The on-screen display controller 7A receives the character display information from the system controller 76, and sets the font character's resolution to 12 dots by 18 lines. The onscreen display controller 7A further receives the character data and converts the same into the digital character signal sequence.
The video signal D/A converter 7B converts the decoded digital signal sequence from the MPEG decoder 78 and the digital character signal sequence from the on-screen display controller 7A into the analog video signals.
The audio signal D/A converter 7C converts the CD-DA signal sequence from the MPEG decoder 78 into the analog audio signals.
Described next is the operation of the optical disc playback apparatus OPC1 for playing back the optical disc Od other than the music CD. For playing back the optical disc Od, the digital signal processor 75 starts demodulation of the digital signals. Then, the digital signal processor 75 outputs the control information and the sub-code information as well as the signal sequence other than the CD-DA signal sequence.
Based on the control information and the sub-code information from the digital signal processor 75, the system controller 76 determines that the signal sequence is other than the CD-DA signal sequence. The system controller 76 also monitors a system error such as track jump and focus error. Whenever such error occurs, the system controller 76 instructs the optical servo controller 74 so that the optical pickup 73 and the spindle motor 72 return to initial states thereof.
The information signal sequence separator 79 separates the digital signal sequences from the digital signal processor 75 into the CD-DA signal sequence and the signal sequence other than that.
The MPEG decoder 78 receives the CD-DA signal sequence and the signal sequence other than that from the information signal sequence separator 79. The MPEG1 decoder 78 converts, in real time, the video signal sequence into the decoded digital signal sequence in the PAL format if the video recorded on the optical disc Od is in the PAL format, and in the NTSC format if in the NTSC format.
The on-screen display controller 7A receives the character display information and the character data from the system controller 76, and converts the character data into the digital character signal sequence to display the on-screen message in the font character of 12 dots by 18 lines.
The video signal D/A converter 7B converts the decoded digital signal sequence from the MPEG decoder 78 and the digital character signal sequence from the on-screen display controller 7A into the analog video signals.
The audio signal D/A converter converts the CD-DA signal sequence from the MPEG decoder 78 into the analog audio signals.
Next, in FIG. 12, a second example of the conventional optical disc playback apparatus is shown. An optical disc playback apparatus OPC2 of the example includes an MPEG decoder 88, in which the MPEG decoder 78 and the on-screen display controller 7A of the optical disc playback apparatus OPC1 shown in FIG. 11 are integrally constructed.
Consequently, the MPEG decoder 88 converts the character display information and the character data from the system controller 76 into the digital character signal sequence. Further, the MPEG decoder 88 can output the converted digital character signal sequence together with the decoded digital signal sequence. Since the operation of the optical disc playback apparatus OPC2 for playing back the optical disc Od is basically the same as that of the optical disc playback apparatus OPC1 except for the above described operation related to the MPEG decoder 88, the description thereof is omitted herein.
As described above, the resolution of television images differ from each other depending on the image data sources and display formats of images recorded thereon. Such differences are described by referring to FIGS. 13, 14, 15, 16, and 17.
In FIG. 13, V and H denote vertical and horizontal resolutions of a television image, respectively. For the sake of distinction, the vertical resolution V and the horizontal resolution H are each provided with a suffix p if the image is in the PAL format and provided with a suffix n if in the NTSC format.
In FIG. 14, with respect to the image in the NTSC format, a resolution and an aspect ratio thereof are shown for each type of optical discs. In FIG. 14, a column OD on the far left end shows types of optical disc, i.e., VCD, SVCD, and DVD. The next column Vn on the right shows the vertical resolutions of images recorded on VCD, SVCD, and DVD, respectively. The vertical resolution Vn of the image on VCD is provided with a suffix V if distinction is required. Similarly, the vertical resolutions Vn of images on SVCD and DVD are provided with suffixes S and D, respectively.
The next column Hn on the right shows the horizontal resolutions of the images recorded on VCD, SVCD, and DVD, respectively. Similarly to the column Vn, the horizontal resolutions Hn of the images on VCD, SVCD, and DVD are respectively provided with suffixes V, S, and D if distinction is required.
The next column Hn/Vn on the right shows the aspect ratios of the images for each type of optical disc. The aspect ratios are shown in numbers rounded off to two decimal places.
The next column Vn/VnV on the right shows the ratios between the vertical resolution VnV of VCD and the vertical resolution Vn of each type optical disc (VnV, VnS, VnD). The ratios are shown in numbers rounded off to two decimal places.
The next column Hn/HnV on the right shows the ratios between the horizontal resolution HnV of VCD and the horizontal resolution Hn of each type optical disc (VnV, VnS, VnD). The ratios are shown in numbers rounded off to two decimal places.
As is shown in FIG. 14, the vertical resolution VnV of the NTSC image on the VCD is 240 lines, the horizontal resolution HnV thereof is 352 dots, and the aspect ratio HnV/VnV thereof is 1.47.
The vertical resolution VnS of the image on the SVCD is 480 lines, the horizontal resolution HnS thereof is 480 dots, and the aspect ratio HnS/VnS thereof is 1. Further, the vertical resolution ratio VnS/VnV=480/240 is 2, and the horizontal resolution ratio HnS/HnV=480/352 is 1.36.
The vertical resolution VnD of the image on the DVD is 480 lines, the horizontal resolution HnD thereof is 720 dots, and the aspect ratio HnD/VnD thereof is 1.5. Further, the vertical resolution ratio VnD/VnV=480/240 is 2, and the horizontal resolution ratio HnD/HnV=720/352 is 2.05.
In FIG. 15, with respect to the image in the PAL format, a resolution and an aspect ratio thereof are shown for each type of optical discs in the similar manner to FIG. 14. In FIG. 15, a column OD on the far left end shows types of optical disc, i.e., VCD, SVCD, and DVD.
The vertical resolution VpV of the PAL image on the VCD is 288 lines, the horizontal resolution HpV thereof is 352 dots, and the aspect ratio HpV/VpV thereof is 1.22.
The vertical resolution VpS of the image on the SVCD is 576 lines, the horizontal resolution HpS thereof is 480 dots, and the aspect ratio HpS/VpS thereof is 0.83. Further, the vertical resolution ratio VpS/VpV=576/288 is 2, and the horizontal resolution ratio HpS/HpV=480/352 is 1.36.
The vertical resolution VpD of the image on the DVD is 576 lines, the horizontal resolution HpD thereof is 720 dots, and the aspect ratio HpD/VpD thereof is 1.25. Further, the vertical resolution ratio VpD/VpV=576/288 is 2, and the horizontal resolution ratio HpD/HpV=720/352 is 2.05.
In FIGS. 16A to 16C, the resolutions, the aspect ratios, and the resolution ratios of the NTSC image in FIG. 14 are relationally shown. In the drawings, screen displays of images are schematically shown for each type of the optical discs. All images are being displayed on the same television monitor and are equal in the vertical image size. On the right side of screen displays, font characters Fn exemplarily displayed in “⋄” are shown. The font characters Fn are all in the resolution of vertically 18 lines and horizontally 12 dots, and are shown in the same up-scaling ratio. For the sake of brevity, hereinafter, “font character” is simply referred to as “font”, unless otherwise distinction is required therebetween.
In FIG. 16A, a screen display SnV of the NTSC image recorded on the VCD (hereinafter, “NTSC-VCD image screen SnV”) and a font FnV displayed thereon as “⋄” are shown. The aspect ratio of the font FnV is approximately 0.67 (12/18) and the aspect ratio HnV/VnV of the NTSC-VCD image screen SnV is 1.47.
Next, as shown in FIG. 16B, with respect to a screen display SnS of the image recorded on the SVCD (hereinafter, “NTSC-SVCD image screen SnS”), the aspect ratio HnS/VnS is 1. The vertical resolution ratio VnS/VnV of the NTSC-SVCD image screen SnS to the NTSC-VCD image screen SnV is 2 and the horizontal resolution ratio HnS/HnV is 1.36.
For each of the images displayed on a television monitor in different resolutions, the vertical and horizontal spaces between the dots are so determined that all images are equal in size in vertical direction. As a result, in comparison with the font FnV, a font FnS displayed on the NTSC-SVCD image screen SnS in 12 dots by 18 lines is shrunk by ½ (240/480) times vertically and by {fraction (1/1.36)} (352/480) times horizontally. The aspect ratio of the font FnS displayed on the NTSC-SVCD image screen SnS is therefore approximately 0.98 (12/18·480/240·352/480).
As such, the font Fn indicating “⋄” is displayed differently on the NTSC-VCD image screen SnV (FnV) and on the NTSC-SVCD image screen SnS (FnS). That is to say, on the NTSC-SVCD image screen SnS, the font Fn is shrunk in size and the aspect ratio thereof is varied from approximately 0.67 to 0.98, resulting in deformation. Also, the size of the font FnS is approximately {fraction (1/2.7)} times smaller than the font FnV.
Next, as shown in FIG. 16C, with respect to a screen display SnD of the image recorded on the DVD (hereinafter, “NTSC-DVD image screen SnD”), the aspect ratio HnD/VnD is 1.5. The vertical resolution ratio VnD/VnV of the NTSC-DVD image screen SnD to the NTSC-VCD image screen SnV is 2 and the horizontal resolution ratio HnD/HnV is 2.05.
As a result, in comparison with the font FnV, a font FnD displayed on the NTSC-DVD image screen SnV in 12 dots by 18 lines is shrunk by ½ (240/480) times vertically and by {fraction (1/2.05)} (352/720) times horizontally. The aspect ratio of the font FnD displayed on the NTSC-DVD image screen SnD is therefore approximately 0.65 (12/18·480/240·352/720).
As such, the font Fn indicating “⋄” is displayed differently on the NTSC-VCD image screen SnV (FnV) and on the NTSC-DVD image screen SnD (FnD). That is to say, on the NTSC-DVD image screen SnD, the font Fn is shrunk in size and the aspect ratio thereof is varied from approximately 0.67 to 0.64. In this case, deformation of the font Fn is not a great concern, but the size of the font FnD is approximately ¼ times smaller than the font FnV.
In FIGS. 17A to 17C, the resolutions, the aspect ratios, and the resolution ratios of the PAL image in FIG. 15 are relationally shown. In the drawings, similarly to FIGS. 16A to 16C, screen displays of images are schematically shown for each type of the optical discs. All images are being displayed on the same television monitor and are equal in the vertical image size. On the right side of screen displays, fonts Fp exemplarily displayed in “⋄” are shown. The fonts Fp are all in the resolution of vertically 18 lines and horizontally 12 dots, and are shown in the same up-scaling ratio.
In FIG. 17A, a screen display SpV of the PAL image recorded on the VCD (hereinafter, “PAL-VCD image screen SpV”) and a font FpV displayed thereon as “⋄” are shown. The aspect ratio of the font FpV is also approximately 0.67 (12/18) and the aspect ratio HpV/VpV of the PAL-VCD image screen SpV is 1.22.
Next, as shown in FIG. 17B, with respect to a screen display SpS of the image recorded on the SVCD (hereinafter, “PAL-SVCD image screen SpS”), the aspect ratio HpS/VpS is 0.83. The vertical resolution ratio VpS/VpV of the PAL-SVCD image screen SpS to the PAL-VCD image screen SpV is 2 and the horizontal resolution ratio HpS/HpV is 1.36.
As a result, in comparison with the font FpV, a font FpS displayed on the PAL-SVCD image screen SpS in 12 dots by 18 lines is shrunk by ½ (288/576) times vertically and by {fraction (1/1.36)} (352/480) times horizontally. The aspect ratio of the font FpS displayed on the PAL-SVCD image screen SpS is therefore approximately 0.97 (12/18·576/288·352/480).
As such, the font Fp indicating “⋄” is displayed differently on the PAL-VCD image screen SpV (FpV) and on the PAL-SVCD image screen SpS (FpS). That is to say, on the PAL-SVCD image screen SpS, the size of the font FpS is approximately 1/2.72 times smaller than the font FpV, and the aspect ratio of the font Fp is varied from approximately 0.67 to 0.97, resulting in deformation.
Next, as shown in FIG. 17C, with respect to a screen display SpD of the image recorded on the DVD (hereinafter, “PAL-DVD image screen SpD”), the aspect ratio HnD/VnD is 1.25. The vertical resolution ratio VpD/VpV of the PAL-DVD image screen SpD to the PAL-VCD image screen SpV is 2 and the horizontal resolution ratio HpD/HpV is 2.05.
As a result, in comparison with the font FpV, a font FpD displayed on the PAL-DVD image screen SpD in 12 dots by 18 lines is shrunk by ½ (288/576) times vertically and by {fraction (1/2.05)} (352/720) times horizontally. The aspect ratio of the font FpD displayed on the PAL-DVD image screen SpD is therefore approximately 0.65 (12/18·576/288·352/720).
As such, the aspect ratio of the font Fp indicating “⋄” is varied from approximately 0.67 to approximately 0.65 between the cases of being displayed on the PAL-VCD image screen SpV (FpV) and on the PAL-DVD image screen SpD (FpD). In this case, deformation of the font Fp is not a great concern, but the size of the font FpD is approximately 1/4.1 times smaller than the font FpV.
As described above, in the conventional optical disc playback apparatus OPC, the resolution remains unchanged for the font indicating characters and symbols displayed as the on-screen message although the resolution of the image on the television varies depending on the disc type or the display format. As a result, with increasing resolution of the television image, the font is shrunk and deformed, and visibility of the on-screen message is considerably impaired.
To be specific, in the conventional optical disc playback apparatus OPC, the font of the on-screen message remains unchanged in low resolution of 12 dots by 18 lines whether the reproduced image is high or low in resolution. Therefore, the problem comes up that if the reproduced image in high-resolution, the on-screen message is apparently displayed in smaller size and impaired in its visibility. Further, the number of pixels composing the font of the on-screen message is small. Therefore, another problem comes up that Chinese characters and symbols in high-resolution can not be displayed. Still further, in the future, further an increase in the resolution of various types of reproduced images is expected with an increase in television image resolution and progression of digital compression technique for moving pictures. The font resolution of the on-screen message therefore will need improvement more than ever.
The present invention aims to solve the problems discussed above and to provide an optical disc playback apparatus for displaying an on-screen message such that each font is displayed in high-visibility without much change in size and form regardless of the resolution of the image. When a VCD, Karaoke CD, SVCD (including CVD), or DVD is played back, information recorded thereon and an image display format of data being reproduced are determined. Based on the determination, the on-screen message is displayed in the font having resolution suitably selected for a type of an optical disc or a resolution of an image.